Lifesaving aircraft rescue operations begin as soon as the aircraft location is known and the amount of rescue effort required is determined. Currently a device called an Emergency Locator Transmitter (ELT) is activated whenever the aircraft experiences a high-G impact (i.e. crashes). ELT's have been in use in aircraft for many years. There are several models but all have basically the same function, i.e. upon activation the ELT transmits a continuous or pulsed signal. There are several limitations to the use of ELT's currently in service. For example:
1) The signal transmitted by the ELT is a continuous wave (CW) signal that is initially detected by satellites or other aircraft. The relative strength of the signal is utilized by multiple receivers in a method called triangulation to determine the approximate location of the transmitting ELT. Triangulation takes time and the time spent triangulating is time not spent providing medical aid. Triangulation typically locates the source of the signal to a 6 mile radius.
2) The magnitude of the rescue effort required is not known until there is a visual sighting or a coincidental overdue aircraft. Most current ELT devices have no method of identifying the source of the signal.
3) Currently, it is estimated that over 95% of ELT activation's are non emergency (inadvertent or otherwise). Due to the cost of a search effort, rescue personnel are not immediately dispatched because of the strong likelihood of a false signal. With a beacon there is no way of knowing if the signal is an accidental or emergency activation. Thus, rescue personnel are not dispatched until the origin of the signal is determined to be of an emergency basis.
4) Because a visual sighting is required, adverse weather conditions can hinder the search efforts.
5) In many instances, the search must be completed successfully before the transmitter depletes the power source because once the ELT stops transmitting, the search effort can no longer utilize the transmitter as a homing signal.
6) In cases where fire or fuel spillage is involved, ELT signals typically last only a few seconds before ELT failure--an inadequate amount of time to triangulate.
7) The condition of the ELT's battery power source is not known until activation. Batteries are merely replaced once a year. The ELT battery may not work at all.